Tanning leather

ABSTRACT

Leather is tanned by cross-linking collagen with tris(hydroxymethyl)phosphine or a condensate of a tetrakis(hydroxymethyl)phosphonium salt with an amide or amine in a main tannage or retannage.

[0001] The present invention relates to a novel process for tanningleather using phosphonium salts. Tanning is a process for thepreservation of skins, by which is meant the collagen-containinginteguments of vertebrates including mammals (e.g. cows, pigs, deer,goats, sheep, seals, antelope, mink, stoats and camels), fish, (e.g.sharks), reptiles (e.g. snakes, lizards and crocodiles), and birds (e.g.ostrich). Skins comprise a layer of collagen, and tanning entailsreacting the collagen with a cross linking, or tanning, agent to crosslink reactive sites within the collagen molecule. The product of thecross linking is leather, which is substantially less susceptible thanskin to bacterial degradation.

[0002] A consequence of the cross linking is an increase in the minimumtemperature at which the wet leather tends to shrink. This shrinktemperature is often used as an indication of the degree of tanning.

[0003] The collagen layer of the skin is separated from fats, connectivetissue and other subcutaneous protein, and optionally from the outerkeratinous layer, by a combination of chemical and physical steps. Theformer may include liming, bating, pickling and/or degreasing.

[0004] The skin is then subjected to treatment in one or more stageswith various tanning agents selected to give the desired end properties.

[0005] The main types of tannage are: vegetable tannage, based on tanninas the active cross linking agent; mineral tannage using variouspolyvalent metal salts, especially salts of chromium, aluminium, iron,or zirconium; and synthetic tanning agents, referred to as “syntans”.Syntans include replacement syntans which are active tanning agentscapable of tanning leather when used as the sole tannage and auxiliarysyntans which are added to other tannages to modify the character of theleather but which are not in themselves active tanning agents. Syntansinclude various polymers and copolymers, such as those obtained bycondensing formaldehyde with, for example, phenols and/or arylsulphonates, and acrylate, methacrylate, acrylamide and/or acrylonitrilehomopolymers and copolymers. Formaldehyde itself and dialdehydes such asglutaraldehyde are also used in tanning, usually in combination withother tannages.

[0006] For centuries the production of leather was based on thevegetable tannages which produce the characteristic brown colourtraditionally associated with leather. One of the first mineral tannageswas alum, but currently the most widely used tanning agent is chrome,usually in the form of basic chromium sulphate, which produces a bluegrey leather with high shrink temperatures. However mineral tannages ingeneral, and chrome tannages in particular are under pressure onenvironmental grounds. Syntans are less environmentally harmful thanmineral tanning agents but typically give an off white or yellowishleather. Formaldehyde and difunctional aldehydes present a health hazardand are unpleasant to handle. Existing, tanning processes cannot readilyprovide a good quality, pure white leather suitable for use as such orfor dyeing, at least using environmentally acceptable and economicallyviable ingredients.

[0007] An object of the invention is to provide an environmentallyacceptable tanning process which can produce white leather with highshrink temperatures e.g. above 80 and preferably above 85°. A furtherobject is to produce a leather which is readily dyed, to give clear,light shades.

[0008] Tetrakis (hydroxymethyl) phosphonium salts which will be referredto generically herein as THP salts have long been used asfire-retardants for textiles and have been applied to the keratinous(fur) side of skins for this purpose. The salts may be applied directlyto the fabric or in the form of precondensates which are water solubleor sparingly water soluble copolymers of THP with organic nitrogencompounds such as urea or an amine. Such copolymers are referred toherein as THP condensates. THP condensates may contain 2 or morephosphorus atoms, so long as the phosphorus compound is water soluble toa concentration of at least 0.5 g/l at 25° C. Such phosphorus compoundscontain a total of at least 2 hydroxymethyl groups, usually at least oneper phosphorus atom, and preferably at least 2 hydroxymethyl groups perphosphorus atom. The group or groups joining the phosphorus atomstogether may be of the formula —R—, —R—O—, —R—O—R—, —R—NH—R or —R—R″—R—where R is an alkylene group of 1 to 4 carbon atoms and R″ is theresidue formed by removal of two hydrogen atoms, bonded to nitrogen,from a di or polyamide or an amine or di or polyamine, such as urea, aC₁₋₂₀ alkylamine, dicyandiamide, thiourea or guanidine. Such compoundswith 2 or more, e.g. 3, hydroxyalkyl groups per phosphorus atom may bemade by self condensation of THP salts with a compound of generalformula R″H₂ such as urea, or a C_(1 to 20) alkylamine, e.g. by heatingat 40 to 120° C. THP salts have also been known as possible ingredientsof tanning liquors for more than thirty six years. U.S. Pat. No.2,992,879 referred to THP chloride (THPC) as an unsatisfactory tanningagent on its own, and recommended a combination of THPC and a phenolsuch as resorcinol speculating that the two react together to form aneffective tanning agent when the pH is raised. In fact THP salts docopolymerise with phenols such as resorcinol (see, for example, TextileResearch Journal, December 1982, P743). U.S. Pat. No. 3,104,151describes the use of such THPC phenol copolymers as light pretannagesfor leather in which the main tannage is vegetable or mineral. GB 2 287953 describes the use of THP salts as cross linkers in conjunction withmelamine formaldehyde or urea formaldehyde prepolymers, in order to forma copolymeric tanning agent in situ in the tanning liquor. EP 0 559 867describes the use of THP sulphate (THPS) on raw or cured skin prior totanning e.g. in acid degreasing. EP 0 681 030 describes the use of THPSas a cross linker for casein finishes applied to leather after tanning.

[0009] THP salts are stable under acidic conditions in the absence ofair or oxidising agents. At pH above 3 and in the absence of oxidisingagents they are gradually converted to the parent base,tris(hydroxymethyl)phosphine herein referred to as THP. Conversion israpid and substantially complete between pH of about 4 and 6. Above pH7, or in the presence of oxidising agents THP salts or THP are convertedto tris(hydroxymethyl)phosphine oxide (THPO), conversion being rapid andsubstantially complete at pH above about 10, e.g. 12. It has been statedthat THPO is an effective tanning agent.

[0010] We have now discovered that contrary to statements in the art,THPO is not an effective main tanning agent for leather, and that THPsalts are also ineffective as main tannages. However we have found thatTHP and THP condensates are both highly effective main tanning agents.THP is most effective when formed in situ by first impregnating theleather with a THP salt, in the substantial absence of monomers orprepolymers which react or copolymerise with THP and raising the pHabove 4 and preferably above 5. THP provides a particularly effectivetanning system, which is ecologically friendly. We have found that THPgives leather which is especially suitable for dyeing. THP is especiallyeffective in combination with syntans. In the absence of other tanningagents, especially vegetable tannages, mineral tannages, aldehydes andphenols the use of THP, alone or with syntans, and especially resinsyntans, results in a particularly white leather.

[0011] The invention provides a method of tanning which comprisesreacting collagen with THP or a THP condensate in a main tannage orretannage.

[0012] According to a preferred embodiment this invention provides amethod of tanning in which skins which have been subjected to partialtanning in a pretanning operation are contacted with a THP salt in thesubstantial absence of a monomer or prepolymer capable of reacting orcopolymerising therewith or of an oxidising agent capable of oxidisingTHP to THPO and at a pH below 4, and the pH is raised above 4,preferably above 4.5, more preferably above 5, most preferably above 5.5e.g. 4 to 7 to form THP but not sufficiently to convert more than 20% ofthe weight of THP into THPO and for a sufficient time to raise theshrink temperature above 80° and preferably above 85°. According to apreferred embodiment the leather is subsequently retained and dyed bycontacting with a solution or dispersion of an appropriate dye.

[0013] According to a further embodiment our invention provides a methodof tanning leather in which skins are contacted either simultaneously orconsecutively, in one or more stages and in any order, with:

[0014] (A) THP in the substantial absence of a monomer or prepolymercapable of copolymerising therewith, and/or a THP condensate; and

[0015] (B) a syntan, preferably a resin syntan.

[0016] In a preferred embodiment skins are tanned in a process involvingan optional pretannage comprising THP, a THP condensate and/or a syntan,a main tannage in which the shrink temperature is raised above 80° C.and preferably above 85° C. and optionally a retannage wherein (A) THPand/or a THP condensate, and (B) a resin syntan are each used in atleast one of the main tannage and the retannage.

[0017] For the purpose of this specification “syntan” is used to referto synthetic organic compounds capable of reacting with collagen to formcross links or to modify the physical properties of the leather and alsoto auxiliary syntans which do not in themselves contribute substantiallyto the cross linking but which modify the physical properties of theleather. For example the term includes any water soluble polymerprepared by copolymerising formaldehyde, which is capable of increasingthe shrink resistance of collagen and which comprises at least two unitsof the formula

[0018] where each M is an aryl group such as a phenyl, naphthyl oraniline group substituted with one or more hydroxyl and/or sulphate,sulphone or sulphonimide groups or a urea or melamine residue. As usedherein the term “syntan” also includes resin syntans which arehomopolymers and copolymers of unsaturated carboxylic acids or theirsalts, esters, amides or nitriles, e.g. acrylic acid, methacrylic acid,acrylamide, acrylonitrile, maleic acid, fumaric acid, itaconic acid,aconitic acid, crotonic acid, isocrotonic acid, citraconic acid,mesaconic acid, angelic acid, tiglic acid and cinnamic acid. Thecopolymers may also comprise other vinylic comonomers such as styrene.Also included are acetone condensates with, for example sulphones andsulphonamides. Resin syntan may modify such properties as dye levelling,filling, grain appearance, break, grain strength, buffing nap, softnessand tensile or tear strength.

[0019] THP may be formed in situ from any THP salt by raising the pH. Itis preferred to use a catalyst for the formation of THP. For example amixture of magnesium salt such as magnesium sulphate with a watersoluble carboxylate salt such as sodium formate, sodium acetate,potassium propiate or other water soluble alkali metal or ammonium saltof a carboxylic acid, preferably the pH is raised above 3.5, morepreferably above 4, e.g. above 4.5. High pH is preferably avoidedbecause it converts THP to THPO, which is substantially ineffective as atanning agent. We prefer that THP solutions for use according to ourinvention should have a pH less than 10, more preferably less than 9,especially less than 8, typically less than 7.5, most preferably 4.5 to7. We prefer that the THP contains less than 15%, more preferably lessthan 10%, e.g. less than 9% of THPO based on the weight thereof.Generally the less THPO present the better.

[0020] The THP salt is preferably the sulphate (THPS), but may also bethe chloride (THPC) or phosphate (THPP). Other salts which could lesspreferably be used include the bromide, sulphite, carbonate, acetate,citrate, formate lactate or borate. In principal, any water soluble THPsalt with an anion which does not interact adversely with the leathermay be used. It is preferred that oxidising agents for THP should besubstantially absent.

[0021] The THP condensate may preferably be a condensate of a THP saltand urea or THP salt with an alkyl amine, e.g. a C₁₋₂₀ alkylamine.Alternatively the THP salt may be condensed with thiourea, guanidine,ammonia, dicyandiamide or with a combination of comonomers. The THP saltis usually THPC or THPS, although any salt of a counterion which doesnot react adversely with other components of the system may be used. TheTHP condensate may be formed in situ by adding THP or a THP salt ande.g. guanidine or dicyandiamide to the tannage.

[0022] The THP salt, THP and THP condensate is preferably used in atotal concentration of from 0.01 to 20% by weight based on the totalweight of the tanning liquor, more preferably 0.5 to 10%, e.g. 1 to 5%,most preferably 1.5 to 4%. The total proportion of the THP salt used ispreferably from 0.3 to 20% by weight based on the weight of wet skin,more preferably 1 to 15%, especially 1.5 to 10%, most preferably 2 to5%.

[0023] In the preferred embodiment, we prefer that the THP or THPcondensate tanned leather, optionally after one or more other tanningstages, is contacted with an acid, basic or direct dye. It is observedthat the rate of uptake of dye from the dyebath is substantiallyincreased in leather which has been tanned using THP or THP condensate.

[0024] When the THP or THP condensate is used in combination with asyntan, the latter is preferably a polyacrylate, polymethacrylate, orcopolymer of acrylic and/or methacrylic acid with acrylonitrile and/oracrylamide. Typically the polymer has a molecular weight in the range1,000 to 200,000, more usually 3,000 to 100,000. Alternatively thesyntan may be or may comprise a copolymer of formaldehyde with a hydroxysubstituted and/or sulphonated benzene, alkyl benzene, naphthalene oralkyl naphthalene such as for example, phenol, benzene sulphonic acid,cresol, toluene sulphonic acid, xylenol, naphthalene sulphonic acid,resorcinol or phenol sulphonic acid, or mixtures, thereof in the form ofrandom or block copolymers.

[0025] The syntan is preferably present at a concentration of from 0.5to 35% by weight of the tanning liquor. e.g. 1 to 20%, more preferably 2to 10% especially 3 to 6%. The total proportion of syntan used ispreferably from 1 to 20% by weight based on the wet weight of skins,e.g. 2 to 10% especially 3 to 5%.

[0026] The proportion by weight of total THP, THP salt and THPcondensate to syntan may typically be from 1:10 to 10:1, preferably 1:5to 2:1, especially 1:2 to 1:1. The total proportion of tannages used ispreferably from 2 to 20% active weight based on the wet weight of skins,e.g. 3 to 10%, especially 4 to 8%. The total tannage used preferablycomprises more than 80% by weight, more preferably more than 90% byweight, e.g. more than 95% of total THP, THP salts, THP condensate andsyntan. Where white leather is required, we prefer that the totaltannages consist essentially of THP and/or THP condensate, and syntan.In particular we prefer the leather is not tanned with vegetable ormineral tannage, with aldehydes or with phenols.

[0027] The THP is applied in the substantial absence of monomers orprepolymers capable of copolymerising with THP such as phenol, urea,melamine or their precondensates with formaldehyde. For the purposes ofthis specification, “the substantial absence of monomers or prepolymers”means less than the minimum that would be capable of reacting orcopolymerising with 50% of the THP, more preferably less than theminimum that would be required to react or copolymerise with 20%, e.g.less than 5% by weight based on the THP salt, most preferably less than2%, especially less than 1%.

[0028] The THP or THP condensate is preferably applied as a firsttanning step with a syntan as a retan. Preferably the THP is applied toacidified skins following aqueous degreasing. E.g. the initial pH istypically below 5, e.g. below 4. We prefer that the pH be raised above 5and preferably maintained above 6 for the main duration of the tanningprocess.

[0029] The skins are preferably agitated in the tanning liquor for asufficient time to raise the shrink temperature above 75° C., morepreferably above 80° C., most preferably above 85° C.

[0030] The tanned skins are typically washed with warm water and fatliquored using a suitable oil or blend of oils. Fat liquoring isnormally carried out after dyeing.

[0031] Penetration of the hide depends on the thickness of the hide andthe pH at which the THP is applied. If the pH of the hide is too lowwhen it is contacted with the THP inadequate take-up of the shrinkinhibitor may occur. If the hide is too thick, penetration may belimited to the outer layers of the leather, leaving untreated areas inthe interior. The extent to which THP has been absorbed by, and haspenetrated, the hide needs to be determined.

[0032] THP users may also wish to be able to check effluents to ensurethat THP has been removed or reduced to acceptable levels prior todischarge. Hitherto the only way of determining the presence of THP hasbeen to take samples and to send them to an analytical laboratory fordetailed analysis. This is a lengthy operation. Since many customers donot have suitably equipped laboratories the results may take days toobtain. Such methods are obviously unsuitable for routine qualitycontrol, and cannot provide the rapid feedback required for processcontrol.

[0033] Unfortunately, we have found that THP does not readily givecharacteristic colour responses to any of the reagents most commonlyused for the calorimetric analysis of organic bases.

[0034] We have now discovered that selenium provides a distinctivebright orange colouration with THP. The selenium is preferably added inthe form of an aqueous solution of a colourless, water soluble,inorganic selenium compound and most preferably an oxyacid such selenicor preferable selenous acid or an oxysalt of selenium such as a selenateor preferably a selenite. The salt is preferably an alkali metal orammonium salt, and most preferably sodium selenite. However, anycolourless salt of selenous acid which is sufficiently soluble may beused.

[0035] Our invention therefore further provides a method of testing aleather to which THP has been applied as a main tannage or retannage oran effluent from such an operation in order to detect the presence ofTHP which comprises applying a colourless water soluble inorganicselenium compound such as selenous acid or its salts thereto.

[0036] Preferably the concentration of selenium compound in theindicator solution is from 0.005 to 20% especially 0.01 to 10% moreespecially 0.05 to 5% e.g. 0.07 to 1%.

[0037] The indicator is preferably added to hides by steeping,injection, spraying, painting or, most conveniently, application with adropper. The indicator is preferably used in proportion of from 0.001 to0.05 g e.g. 0.005 to 0.01 g per cm² of surface.

[0038] In aqueous samples the indicator compound is preferably added ina concentration of from 10 to 10000 ppm based on the sample, e.g. 100 to5000 ppm especially 500 to 2000 ppm.

[0039] The indicator solution is preferably aqueous and may have anacid, alkaline or neutral pH. For example the solution may be stronglyacidified with mineral acid such as sulphuric, hydrochloric or nitric.One convenient form of indicator is an analytical standard comprising 1gm per litre selenium as selenous acid in molar nitric acid.

[0040] Alternatively, the indicator may be a neutral or alkalinesolution comprising a salt of selenous acid such as sodium selenite. Ingeneral the colour develops most strongly in samples having a pH greaterthan 3.

[0041] The dye is characterised spectrophotometrically by an absorptionpeak at 300 nm.

[0042] The invention is illustrated by the following examples in whichall percentages are by weight based on the wet weight of skins unlessstated to the contrary:

EXAMPLE 1

[0043] Degreased sheepskins were placed in a rotating drum with 80%water and 8% sodium chloride for 15 minutes. The pH was 3.4. To the drumwas added 10% of a solution containing 25% by weight based on the weightof said solution of THPS. After 60 minutes the pH of the liquor wasraised slowly to 6.5 and tanning continued for a further 2 hours. Theshrink temperature of the partly tanned leather was measured at 86° C.4% of a phenol formaldehyde polymer, for example products sold under the“ELTESOL” or “NEOSYN” CPP 48 Registered Trade Marks, which are a white,light-fast syntan was then added to the leather. After a further 60minutes, the leather was washed with 200% warm (55° C.) water for 15minutes and drained. The wash cycle was repeated.

[0044] The washed leather was fat liquored with a sulphated oil soldunder the Registered Trade Mark “REMSYNOL” ESA and a sulphited fish oilunder the Registered Trade Mark “REMSYNOL” ESI. The pH was adjusted to3.6 with formic acid and the leather horsed until dry.

[0045] The leather was assessed as exceptionally full with a mellowhandle, fully light-fast and with high tensile and tear strengths andhigh shrink temperature:

[0046] Tensile strength (1.4 mm) 180 Kg cm⁻² in perpendicular andparallel directions

[0047] Banmann tear strength (1.4 mm) 12 Kg

[0048] Final shrink temperature=92° C.

EXAMPLE 2

[0049] Degreased skins were subjected to the following sequences:

[0050] (i) 10 mins rotation at pH=5.2 with 5% magnesium sulphate and 2%sodium acetate and 100% water.

[0051] (ii) Addition of 1% of a 2:1 THPC/urea precondensate availablefrom Albright & Wilson UK Limited under its registered Trade Mark“PROBAN” CC followed by 90 mins rotation at pH=4.5. The shrinktemperature was elevated to 59° C. Testing a sample with seleniumindicator gave a pale orange colour evenly distributed through thesample indicating even penetration.

[0052] (iii) The pH was raised to 5.8 by addition of 1% sodium carbonateand the shrink temperature rose to 71° C. The selenium indicator gave abright orange colouration evenly distributed through the sample.

[0053] (iv) The pH was raised to 6.8 by addition of 0.75% sodiumcarbonate to give a shrink temperature of 84° C. The leather was tightwith no visible case hardening.

[0054] No further elevation of shrinkage temperature could be obtainedon addition of more carbonate.

EXAMPLE 3

[0055] THP condensate was used to enhance tanning by THP.

[0056] The process of Example 1 was repeated using 1% of a 75% aqueoussolution of THPS in place of THP condensate in stage (ii) as a control.The maximum shrink temperature obtained was 80-81° C. The process wasrepeated, but using a mixture of 1% of a THP condensate comprising 3:1THPC and urea reacted with a C₁₆₋₁₈ amine, and 1% of 75% THPS as theaddition in stage (ii). The THP condensate is available from Albright &Wilson UK Limited under its registered Trade Mark “PROBAN” ST. Theleather had a shrink temperature of 85° C. and a full, tight feel.

EXAMPLE 4

[0057] Example 1 was repeated using in step (ii) a mixture of 0.5% ofthe THP condensate of Example 1 and 0.5% of the THP condensate ofExample 2 The shrink temperature was 74° C.

EXAMPLE 5

[0058] Following treatment with magnesium sulphate and sodium acetate asin stage (i) of Example 1, the skins were rotated for 2 hours with amixture of 1% of the THP condensate of Example 1 and 1% of a 75% aqueoussolution of THPS. The pH fell to 2.9, selenium indicator showed verypale yellow on flesh side only indicating poor penetration. Shrinktemperature was 58° C. On basification with sodium carbonate to pH 6.5the shrink temperature rose to 83° C. Selenium indicator gave an evenlydistributed bright orange colour. The leather was of high quality, fulland with a tight feel.

EXAMPLE 6

[0059] Example 4 was repeated replacing the THP condensate of Example 1with that of Example 2. A similar product was obtained at pH 6.5 with ashrink temperature of 84° C.

EXAMPLE 7

[0060] Wet blue sheepskins were retanned as follows:

[0061] Wash

[0062] 200% Water @ 35° C.

[0063] 10′

[0064] Drain

[0065] Repeat

[0066] 100 Water @ 35° C.

[0067] 5% “ALBRITE” AD

[0068] 45′

[0069] 1.5% Ammonium Bicarbonate

[0070] 0.5% Sodium Formate

[0071] 40′

[0072] pH 5.6 (through cross section)

[0073] Wash

[0074] 200% Water @ 50° C.

[0075] 10′

[0076] Drain

[0077] Repeat

[0078] 100% Water @ 50° C.

[0079] 2% Dyestuff

[0080] 40′

[0081] 6% “REMSYNOL” ESA

[0082] 4% “REMSYNOL” ESI

[0083] 40′

[0084] Adjust pH to 3.4 with formic acid

[0085] Horse up

[0086] Dry and finish

[0087] “ALBRITE” and “REMSYNOL” are registered trademarks

[0088] “ALBRITE” AD is an aqueous solution of THP sulphate

EXAMPLE 8

[0089] Wet salted sheepskins were treated as follows:

[0090] All floats were approximately 500%:

[0091] 1st scour

[0092] Water @ 35° C.

[0093] 1 g/l Wetting agent

[0094] 0.5 g/l Sodium Carbonate

[0095] 30′

[0096] Drain

[0097] Flesh

[0098] Water @ 35° C.

[0099] 1 g/l Wetting agent

[0100] 2 g/l Bating agent

[0101] 0.5 g/l Sodium Metabisulphate

[0102] 60′

[0103] Drain

[0104] Wash

[0105] Drain

[0106] Hydro

[0107] Shear wool to required length

[0108] Pickle

[0109] Water @ 20° C.

[0110] 50 g/l Salt

[0111] 10′

[0112] 2.5 g/l Formic Acid

[0113] 0.7 g/l Sulphuric Acid

[0114] 120′

[0115] Leave overnight with intermittent running pH 2.8-3.0

[0116] Add 12 g/l “ALBRITE” AD

[0117] 10′

[0118] 4 g/l Sulphited oil (electrolyte stable)

[0119] 360′

[0120] Leave overnight

[0121] Check shrinkage temp

[0122] Basify to pH 6.5 with additions of sod carbonate

[0123] Check shrinkage temp

[0124] Drain

[0125] Rinse horse

[0126] Crust out

[0127] Butt and stake

EXAMPLE 9

[0128] Line split English 26K Ox hides were tanned as follows:

[0129] Wash

[0130] 200% Water @ 30° C.

[0131] 10′

[0132] Drain

[0133] Repeat

[0134] 200% Water @ 35° C.

[0135] 2% Ammonium Chloride

[0136] 0.5% Sodium Metabisulphate

[0137] 60′

[0138] pH 8.3 (through cross section)

[0139] 1% “PANCREOL” PBW1 (Pancreatic bate)

[0140] 45′

[0141] Drain

[0142] Wash

[0143] 200% Water @ 20° C.

[0144] 10′

[0145] Drain

[0146] Repeat

[0147] 80% Water @ 20° C. Salt

[0148] 8% Salt

[0149] 10′

[0150] “PANCREOL” is a registered trademark

[0151] 6° Bé

[0152] 1.2% Sulphuric Acid

[0153] 0.4% Formic

[0154] 3 hours

[0155] 6° Bé

[0156] 2.8 pH

[0157] Add

[0158] 10 “ALBRITE” AD

[0159] 2 hours

[0160] Complete penetration

[0161] ADD

[0162] 1.5% Sodium Carbonate

[0163] 60′

[0164] 1.5% Sodium Carbonate

[0165] 60′

[0166] pH 6.8

[0167] Run for a further 3 hours

[0168] T_(s)° C. 89° C.

[0169] Horse up

[0170] Samm

[0171] Shave

[0172] Wash

[0173] 200% Water @ 50° C.

[0174] 10′

[0175] Drain

[0176] Repeat

[0177] 100% Water @ 50° C.

[0178] 5% “NEOSYN” AC4 (acrylic resin)

[0179] 40′

[0180] 2% Dyestuff

[0181] 40′

[0182] “NEOSYN” is a registered trademark

[0183] 6% “REMSYNOL” ESA

[0184] 4% “REMSYNOL” ESI

[0185] 40′

[0186] Adjust pH to 3.6 with formic acid

EXAMPLE 10

[0187] Leather was produced by the method Example 9 except thatretannage and dyeing were as follows:

[0188] 150% Water @ 45° C.

[0189] 5% Mimosa

[0190] 4% “NEOSYN” RW

[0191] 45′

[0192] 4% Dyestuff

[0193] 45′

[0194] 4% “REMSYNOL” ESA

[0195] 4% “REMSYNOL” ESI

[0196] 40′

[0197] Adjust pH to 3.4 with formic acid

EXAMPLE 11

[0198] English degreased pickled sheepskins were tanned as follows:

[0199] 80% Water

[0200] 8% Salt

[0201] 15 minutes

[0202] pH 3.4

[0203] 6° Bé

[0204] 10% “ALBRITE” AD

[0205] 60 minutes

[0206] Raise pH slowly to 6.5

[0207] 120 minutes

[0208] Run 120 minutes @ 6.5

[0209] Shrinkage temperature 86° C.

[0210] Retan

[0211] ADD

[0212] 4% “NEOSYN” CPP48 (white, light fast syntan)

[0213] 60′

[0214] Wash

[0215] 200% Water @ 55° C.

[0216] 15′

[0217] Drain

[0218] Repeat

[0219] 100% Water @ 55° C.

[0220] 6% “REMSYNOL” ESI

[0221] 4% “REMSYNOL” ESA

[0222] 4% White Pigment

[0223] 45′

[0224] Adjust pH to 3.6 with formic acid

[0225] Horse up overnight

[0226] Dry

EXAMPLE 12

[0227] English degreased pickled sheepskins were tanned as follows:

[0228] 80% Water

[0229] 8% Salt

[0230] 15 minutes

[0231] pH 3.4

[0232] 6° Bé

[0233] 3.1 “ALBRITE AD75M”

[0234] 60 minutes

[0235] Raise pH slowly to 6.5

[0236] 120 minutes

[0237] Run 120 minutes @ 6.5

[0238] Shrinkage temperature 84° C.

[0239] Retan

[0240] “ALBRITE AD75M” is an aqueous solution of THP sulphate

[0241] ADD 4% “DEHSCOFIX” 914

[0242] Wash

[0243] 200% Water @ 55° C.

[0244] 15′

[0245] Drain

[0246] Repeat

[0247] 100% Water @ 55° C.

[0248] 5% “REMSYNOL” ESI

[0249] 5% “REMSYNOL” ESA

[0250] 45′

[0251] Adjust pH to 3.4 with formic acid

[0252] Horse up overnight

[0253] Dry

EXAMPLE 13

[0254] English degreased pickled sheepskins were tanned as follows:

[0255] 80% Water

[0256] 8% Salt

[0257] 15 minutes

[0258] pH 3.4

[0259] 6° Bé

[0260] 3% “ALBRITE AD75M”

[0261] 60 minutes

[0262] Raise pH slowly to 6.5

[0263] Run 120 minutes @ 6.5

[0264] Shrinkage temperature 84° C.

[0265] Retan

[0266] ADD 4% “NEOSYN” DSF2

[0267]60′

[0268] Wash

[0269] 200% Water @ 55° C.

[0270] Drain

[0271] “DEHSCOFIX” is a registered trademark

[0272] Repeat

[0273] 100% Water @ 55° C.

[0274] 5% “REMSYNOL” ESI

[0275] 5% “REMSYNOL” ESA

[0276] 45′

[0277] Adjust pH to 3.6 with formic acid

[0278] Horse up overnight

[0279] Dry

1. A method of tanning which comprises reacting collagen with THP or aTHP condensate in a main tannage or retannage.
 2. A method of tanningaccording to claim 1 in which skins which have been subjected to partialtanning in a pretanning operation are contacted with a THP salt in thesubstantial absence of a monomer or prepolymer capable of reacting orcopolymerising therewith or of an oxidising agent capable of oxidisingTHP to THPO and at a pH below 5, and the pH is raised sufficiently toform THP but not sufficiently to convert more than 20% of the weight ofTHP into THPO and for a sufficient time to raise the shrink temperatureabove 80° and preferably above 85°.
 3. A method of tanning according toeither of claims 1 and 2 in which skins are contacted eithersimultaneously or consecutively, in one or more stages and in any order,with: (A) THP in the substantial absence of a monomer or prepolymercapable of copolymerising therewith, and/or a THP condensate; and (B) asyntan.
 4. A method of tanning according to any foregoing claim whereinskins are tanned in a process involving an optional pretannagecomprising THP, a THP condensate and/or a syntan, a main tannage inwhich the shrink temperature is raised above 80° C. and preferably above85° C. and optionally a retannage wherein (A) THP and/or a THPcondensate, and (B) a resin syntan are each used in at least one of themain tannage and the retannage.
 5. A method according to any foregoingclaim wherein the leather is subsequently dyed by contacting with asolution or dispersion of an appropriate dye.
 6. A method according toclaim 5 wherein the leather is contacted with an acid, basic or directdye.
 7. A method according to any of claims 3 to 5 wherein the syntan isa resin syntan.
 8. A method according to any of claims 2 to 6 whereintannage comprises a catalyst for the formation of THP.
 9. A methodaccording to any foregoing claim wherein the THP and THP condensates areused in a total concentration based on the wet weight of the skins offrom 0.3 to 20%.
 10. A method according to any foregoing claim wherein asyntan is used in proportion of from 1 to 20% based on the wt weight ofthe skins.
 11. A method according any foregoing claim wherein theproportion by weight of THP to syntan is from 1:10 to 10:1.
 12. A methodaccording to any foregoing claim wherein the total proportion of tannageis from 2 to 20% active weight based on the wet weight of the skins. 13.A method according to any foregoing claim wherein the THP and/or THPcondensate and syntan comprise more than 90% of the total active weightof tannage.
 14. A method according to any foregoing claim wherein themain tannage consists essentially of THP or a THP condensate and theretannage consists essentially of a syntan.
 15. A method according toany foregoing claim wherein the penetration of THP into the hides istested by applying to a sample a solution of selenous acid or a watersoluble selenite.